We have got KASAN splat when tried to set /proc/sys/fs/file-max:
BUG: KASAN: global-out-of-bounds in __do_proc_doulongvec_minmax+0x3e4/0x8f0
Read of size 8 at addr ffff20000f9b2980 by task file-max.sh/36819
Call trace:
dump_backtrace+0x0/0x3f8
show_stack+0x3c/0x60
dump_stack+0x150/0x1a8
print_address_description+0x2b8/0x5a0
kasan_report+0x278/0x648
__asan_load8+0x124/0x170
__do_proc_doulongvec_minmax+0x3e4/0x8f0
proc_doulongvec_minmax+0x80/0xa0
proc_sys_call_handler+0x188/0x2a0
proc_sys_write+0x5c/0x80
__vfs_write+0x118/0x578
vfs_write+0x184/0x418
ksys_write+0xfc/0x1e8
__arm64_sys_write+0x88/0xa8
el0_svc_common+0x1a4/0x500
el0_svc_handler+0xb8/0x180
el0_svc+0x8/0xc
The buggy address belongs to the variable:
zero+0x0/0x40
The cause is that proc_doulongvec_minmax() is trying to cast an int
pointer (namely &zero) to a unsigned long pointer, and dereferencing it.
Although the warning seems does no harm, because zero will be placed
in a .bss section, but it's better to kill the KASAN warning by
redefining zero as a unsigned long, so it's OK whenever it is accessed
as an int or a a unsigned long.
An alternative fix seems to be set the minimal value of file-max to be 1,
so one_ul can be used instead, but I'm not sure whether or not a file-max
with a value of zero has special purpose (e.g., prohibit the file-related
activities of all no-privileged users).
Signed-off-by: Hou Tao <[email protected]>
---
kernel/sysctl.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index e5da394d1ca3..03846e015013 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -124,7 +124,7 @@ static int sixty = 60;
static int __maybe_unused neg_one = -1;
-static int zero;
+static unsigned long zero;
static int __maybe_unused one = 1;
static int __maybe_unused two = 2;
static int __maybe_unused four = 4;
--
2.16.2.dirty
On Thu, Apr 4, 2019 at 11:48 PM Hou Tao <[email protected]> wrote:
>
> We have got KASAN splat when tried to set /proc/sys/fs/file-max:
>
> BUG: KASAN: global-out-of-bounds in __do_proc_doulongvec_minmax+0x3e4/0x8f0
> Read of size 8 at addr ffff20000f9b2980 by task file-max.sh/36819
>
> Call trace:
> dump_backtrace+0x0/0x3f8
> show_stack+0x3c/0x60
> dump_stack+0x150/0x1a8
> print_address_description+0x2b8/0x5a0
> kasan_report+0x278/0x648
> __asan_load8+0x124/0x170
> __do_proc_doulongvec_minmax+0x3e4/0x8f0
> proc_doulongvec_minmax+0x80/0xa0
> proc_sys_call_handler+0x188/0x2a0
> proc_sys_write+0x5c/0x80
> __vfs_write+0x118/0x578
> vfs_write+0x184/0x418
> ksys_write+0xfc/0x1e8
> __arm64_sys_write+0x88/0xa8
> el0_svc_common+0x1a4/0x500
> el0_svc_handler+0xb8/0x180
> el0_svc+0x8/0xc
>
> The buggy address belongs to the variable:
> zero+0x0/0x40
>
> The cause is that proc_doulongvec_minmax() is trying to cast an int
> pointer (namely &zero) to a unsigned long pointer, and dereferencing it.
>
> Although the warning seems does no harm, because zero will be placed
> in a .bss section, but it's better to kill the KASAN warning by
> redefining zero as a unsigned long, so it's OK whenever it is accessed
> as an int or a a unsigned long.
>
> An alternative fix seems to be set the minimal value of file-max to be 1,
> so one_ul can be used instead, but I'm not sure whether or not a file-max
> with a value of zero has special purpose (e.g., prohibit the file-related
> activities of all no-privileged users).
>
> Signed-off-by: Hou Tao <[email protected]>
Acked-by: Kees Cook <[email protected]>
-Kees
> ---
> kernel/sysctl.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sysctl.c b/kernel/sysctl.c
> index e5da394d1ca3..03846e015013 100644
> --- a/kernel/sysctl.c
> +++ b/kernel/sysctl.c
> @@ -124,7 +124,7 @@ static int sixty = 60;
>
> static int __maybe_unused neg_one = -1;
>
> -static int zero;
> +static unsigned long zero;
> static int __maybe_unused one = 1;
> static int __maybe_unused two = 2;
> static int __maybe_unused four = 4;
> --
> 2.16.2.dirty
>
--
Kees Cook
On Fri, Apr 05, 2019 at 02:52:17PM +0800, Hou Tao wrote:
> We have got KASAN splat when tried to set /proc/sys/fs/file-max:
Matteo Croce already has a patch in-flight for this.
Hi,
Cc Andrew for patch inclusion
On 2019/4/6 0:27, Matthew Wilcox wrote:
> On Fri, Apr 05, 2019 at 02:52:17PM +0800, Hou Tao wrote:
>> We have got KASAN splat when tried to set /proc/sys/fs/file-max:
>
> Matteo Croce already has a patch in-flight for this.
>
>
Yes, I find it now: https://lkml.org/lkml/2019/3/28/320. And the fix posted
by Matteo has also been acked by Kees and has the Fixes tag.
So Andrew, could you please take Matteo's patch in your tree ?
Regards,
Tao